Polymeric additives for enhancement of treatment fluids comprising viscoelastic surfactants and methods of use

ABSTRACT

Polymeric additives used with viscoelastic surfactants, fluids comprising such additives and viscoelastic surfactants, and associated methods of use, are provided. In one embodiment, the methods comprise: providing a treatment fluid that comprises an aqueous base fluid, a viscoelastic surfactant, and an amphiphilic polymer, the amphiphilic polymer comprising a hydrophobic component, and a hydrophilic component comprising at least 15 monomer units; and introducing the treatment fluid into at least a portion of a subterranean formation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of U.S. patentapplication Ser. No. 12/551,334, entitled “Treatment Fluids ComprisingTransient Polymer Networks,” filed on Aug. 31, 2009, the entirety ofwhich is herein incorporated by reference, and from which priority isclaimed pursuant to 35 U.S.C. §120.

BACKGROUND

The present invention relates to methods and compositions that may beuseful in treating subterranean formations, and more specifically, topolymeric additives used with viscoelastic surfactants, fluidscomprising such additives and viscoelastic surfactants, and associatedmethods of use.

Viscosified treatment fluids may be used in a variety of subterraneantreatments. As used herein, the term “treatment,” or “treating,” refersto any subterranean operation that uses a fluid in conjunction with adesired function and/or for a desired purpose. The term “treatment,” or“treating,” does not imply any particular action by the fluid. Examplesof common subterranean treatments include, but are not limited to,drilling operations, pre-pad treatments, fracturing operations,perforation operations, preflush treatments, afterflush treatments, sandcontrol treatments (e.g., gravel packing), acidizing treatments (e.g.,matrix acidizing or fracture acidizing), diverting treatments, cementingtreatments, and well bore clean-out treatments. For example, in certainfracturing treatments generally a treatment fluid (e.g., a fracturingfluid or a “pad fluid”) is introduced into a well bore that penetrates asubterranean formation at a sufficient hydraulic pressure to create orenhance one or more pathways, or “fractures,” in the subterraneanformation. These cracks generally increase the permeability of thatportion of the formation. The fluid may comprise particulates, oftenreferred to as “proppant particulates,” that are deposited in theresultant fractures. The proppant particulates are thought to helpprevent the fractures from fully closing upon the release of thehydraulic pressure, forming conductive channels through which fluids mayflow to a well bore penetrating the formation.

Treatment fluids are also utilized in sand control treatments, such asgravel packing. In “gravel-packing” treatments, a treatment fluidsuspends particulates (commonly referred to as “gravel particulates”),and at least a portion of those particulates are then deposited in adesired area in a well bore, e.g., near unconsolidated or weaklyconsolidated formation zones, to form a “gravel pack,” which is agrouping of particulates that are packed sufficiently close together soas to prevent the passage of certain materials through the gravel pack.This “gravel pack” may, inter alia, enhance sand control in thesubterranean formation and/or prevent the flow of particulates from anunconsolidated portion of the subterranean formation (e.g., a proppedfracture) into a well bore. One common type of gravel-packing operationinvolves placing a sand control screen in the well bore and packing theannulus between the screen and the well bore with the gravelparticulates of a specific size designed to prevent the passage offormation sand. The gravel particulates act, inter alia, to prevent theformation sand from occluding the screen or migrating with the producedhydrocarbons, and the screen acts, inter alia, to prevent theparticulates from entering the well bore. The gravel particulates alsomay be coated with certain types of materials, including resins,tackifying agents, and the like. Once the gravel pack is substantiallyin place, the viscosity of the treatment fluid may be reduced to allowit to be recovered. In some situations, fracturing and gravel-packingtreatments are combined into a single treatment (commonly referred to as“FRAC PAC™” operations). In such “FRAC PAC™” operations, the treatmentsare generally completed with a gravel pack screen assembly in place withthe hydraulic fracturing treatment being pumped through the annularspace between the casing and screen. In this situation, the hydraulicfracturing treatment ends in a screen-out condition, creating an annulargravel pack between the screen and casing. In other cases, thefracturing treatment may be performed prior to installing the screen andplacing a gravel pack.

Maintaining sufficient viscosity in treatment fluids may be importantfor a number of reasons. Viscosity is desirable in drilling operationssince treatment fluids with higher viscosity can, among other things,transport solids, such as drill cuttings, more readily. Maintainingsufficient viscosity is important in fracturing treatments forparticulate transport, as well as to create or enhance fracture width.Particulate transport is also important in sand control treatments, suchas gravel packing. Maintaining sufficient viscosity may be important tocontrol and/or reduce leak-off into the formation, improve the abilityto divert another fluid in the formation, and/or reduce pumpingrequirements by reducing friction in the well bore. At the same time,while maintaining sufficient viscosity of a treatment fluid often isdesirable, it also may be desirable to maintain the viscosity of thetreatment fluid in such a way that the viscosity may be reduced at aparticular time, inter alia, for subsequent recovery of the fluid fromthe formation.

To provide the desired viscosity, polymeric gelling agents commonly areadded to the treatment fluids. The term “gelling agent” is definedherein to include any substance that is capable of increasing theviscosity of a fluid, for example, by forming a gel. Examples ofcommonly used polymeric gelling agents include, but are not limited toguar gums and derivatives thereof, cellulose derivatives, biopolymers,and the like. The use of polymeric gelling agents, however, may beproblematic. For instance, these polymeric gelling agents may leave anundesirable gel residue in the subterranean formation after use, whichcan impact permeability. As a result, costly remedial operations may berequired to clean up the fracture face and proppant pack. Foamedtreatment fluids and emulsion-based treatment fluids have been employedto minimize residual damage, but increased expense and complexity oftenhave resulted.

To combat perceived problems associated with polymeric gelling agents,some surfactants have been used as gelling agents. It is well understoodthat, when mixed with an aqueous fluid in a concentration above thecritical micelle concentration, the molecules (or ions) of surfactantsmay associate to form micelles. The term “micelle” is defined to includeany structure that minimizes the contact between the lyophobic(“solvent-repelling”) portion of a surfactant molecule and the solvent,for example, by aggregating the surfactant molecules into structuressuch as spheres, cylinders, or sheets, wherein the lyophobic portionsare on the interior of the aggregate structure and the lyophilic(“solvent-attracting”) portions are on the exterior of the structure.These micelles may function, among other purposes, to stabilizeemulsions, break emulsions, stabilize a foam, change the wettability ofa surface, solubilize certain materials, and/or reduce surface tension.When used as a gelling agent, the molecules (or ions) of the surfactantsused associate to form micelles of a certain micellar structure (e.g.,rodlike, wormlike, vesicles, etc., which are referred to herein as“viscosifying micelles”) that, under certain conditions (e.g.,concentration, ionic strength of the fluid, etc.) are capable of, interalia, imparting increased viscosity to a particular fluid and/or forminga gel. Certain viscosifying micelles may impart increased viscosity to afluid such that the fluid exhibits viscoelastic behavior (e.g., shearthinning properties) due, at least in part, to the association of thesurfactant molecules contained therein. As used herein, the term“viscoelastic surfactant fluid” refers to fluids that exhibit or arecapable of exhibiting viscoelastic behavior due, at least in part, tothe association of surfactant molecules contained therein to formviscosifying micelles.

However, the use of surfactants as gelling agents may be problematic inseveral respects. In certain applications, large quantities ofviscoelastic surfactants may be required to impart the desiredrheological properties to a fluid. Certain viscoelastic surfactants maybe less soluble in certain fluids, which may impair the ability of thosesurfactants to form viscosifying micelles. Viscoelastic surfactantfluids also may be unstable at high temperatures and/or in high saltconcentrations due to, among other things, the tendency of high saltconcentrations to “screen out” electrostatic interactions betweenviscosifying micelles.

SUMMARY

The present invention relates to methods and compositions that may beuseful in treating subterranean formations, and more specifically, topolymeric additives used with viscoelastic surfactants, fluidscomprising such additives and viscoelastic surfactants, and associatedmethods of use.

In one embodiment, the present invention provides a method comprising:providing a treatment fluid that comprises an aqueous base fluid, aviscoelastic surfactant, and an amphiphilic polymer, the amphiphilicpolymer comprising a hydrophobic component, and a hydrophilic componentcomprising at least 15 monomer units; and introducing the treatmentfluid into at least a portion of a subterranean formation.

In another embodiment, the present invention provides a methodcomprising: providing a treatment fluid that comprises an aqueous basefluid, a viscoelastic surfactant, and an amphiphilic polymer, theamphiphilic polymer comprising an alkyl ethoxylate, wherein thetreatment fluid does not comprise a substantial amount of a zwitterionicsurfactant; and introducing the treatment fluid into at least a portionof a subterranean formation.

In another embodiment, the present invention provides a methodcomprising: providing a treatment fluid that comprises an aqueous basefluid, a viscoelastic surfactant, and an amphiphilic polymer, whereinthe treatment fluid does not comprise a substantial amount of azwitterionic surfactant and the amphiphilic polymer comprises: ahydrophobic component selected from the group consisting of: an alkylgroup, a polybutadiene group, a polyisoprene group, a polystyrene group,a polyoxystyrene group, any derivative thereof, and any combinationthereof; and a hydrophilic component selected from the group consistingof a polyethylene oxide group; a polyacrylic acid group, apolyethylacetate group, a dimethylacrylamide group, ann-isopropylacrylamide group, a polyvinylpyrrolidone group, apolyethyleneimine group, any derivative thereof, and any combinationthereof; and introducing the treatment fluid into at least a portion ofa subterranean formation.

In another embodiment, the present invention provides a methodcomprising: providing an aqueous base fluid, a viscoelastic surfactant,and an amphiphilic polymer, the amphiphilic polymer comprising ahydrophobic component, and a hydrophilic component comprising at least15 monomer units; and mixing the aqueous base fluid, the viscoelasticsurfactant, and the amphiphilic polymer together to form a treatmentfluid.

In another embodiment, the present invention provides a treatment fluidcomprising: an aqueous base fluid, a viscoelastic surfactant; and anamphiphilic polymer that comprises a hydrophobic component, and ahydrophilic component comprising at least 15 monomer units.

In another embodiment, the present invention provides a subterraneantreatment additive comprising: a viscoelastic surfactant; and anamphiphilic polymer that comprises a hydrophobic component, and ahydrophilic component comprising at least 15 monomer units.

The features and advantages of the present invention will be readilyapparent to those skilled in the art. While numerous changes may be madeby those skilled in the art, such changes are within the spirit of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

These drawings illustrate certain aspects of some of the embodiments ofthe present invention, and should not be used to limit or define theinvention.

FIGS. 1-8 illustrate data regarding the zero-shear viscosity of certainviscoelastic surfactant fluids, including certain embodiments of thetreatment fluids of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates to methods and compositions that may beuseful in treating subterranean formations, and more specifically, topolymeric additives used with viscoelastic surfactants, fluidscomprising such additives and viscoelastic surfactants, and associatedmethods of use.

The fluids and additives of the present invention generally comprise aviscoelastic surfactant and an amphiphilic polymer that comprises ahydrophobic component and a hydrophilic component. The term“viscoelastic surfactant” is defined herein to include any surfactantthat imparts or is capable of imparting viscoelastic behavior to a fluiddue, at least in part, to the association of surfactant molecules toform viscosifying micelles.

Among the many potential advantages of the present invention, themethods and compositions of the present invention may, among otherthings, enhance the viscoelasticity, stability, and/or other rheologicalproperties of viscoelastic surfactant fluids, particularly at hightemperatures and/or in brines or other high salinity conditions (greaterthan about 0.5 M). The methods of the present invention also may enhancethe solubility of certain viscoelastic surfactants in a fluid, which mayenhance the viscoelasticity, stability, and/or other rheologicalproperties of the resulting viscoelastic surfactant fluid. Moreover, themethods and compositions of the present invention may facilitate theachievement of desired rheological properties in a fluid while utilizinglower concentrations of viscoelastic surfactant.

The viscoelastic surfactants used in the present invention may compriseany viscoelastic surfactant known in the art, any derivative thereof, orany combination thereof. These viscoelastic surfactants may be cationic,anionic, nonionic or amphoteric in nature. The viscoelastic surfactantsmay comprise any number of different compounds, including methyl estersulfonates (e.g., as described in U.S. Pat. Nos. 7,299,874, 7,159,659,and 7,303,019 and U.S. Published Application No. 2006/0183646, therelevant disclosures of which are incorporated herein by reference),hydrolyzed keratin (e.g., as described in U.S. Pat. No. 6,547,871, therelevant disclosure of which is incorporated herein by reference),sulfosuccinates, taurates, amine oxides, ethoxylated amides, alkoxylatedfatty acids, alkoxylated alcohols (e.g., lauryl alcohol ethoxylate,ethoxylated nonyl phenol), ethoxylated fatty amines, ethoxylated alkylamines (e.g., cocoalkylamine ethoxylate), betaines, modified betaines,alkylamidobetaines (e.g., cocoamidopropyl betaine), quaternary ammoniumcompounds (e.g., trimethyltallowammonium chloride, trimethylcocoammoniumchloride), derivatives thereof, and combinations thereof. The term“derivative” is defined herein to include any compound that is made fromone of the listed compounds, for example, by replacing one atom in thelisted compound with another atom or group of atoms, rearranging two ormore atoms in the listed compound, ionizing the listed compounds, orcreating a salt of the listed compound.

Suitable viscoelastic surfactants may comprise mixtures of severaldifferent compounds, including but not limited to: mixtures of anammonium salt of an alkyl ether sulfate, a cocoamidopropyl betainesurfactant, a cocoamidopropyl dimethylamine oxide surfactant, sodiumchloride, and water; mixtures of an ammonium salt of an alkyl ethersulfate surfactant, a cocoamidopropyl hydroxysultaine surfactant, acocoamidopropyl dimethylamine oxide surfactant, sodium chloride, andwater; mixtures of an ethoxylated alcohol ether sulfate surfactant, analkyl or alkene amidopropyl betaine surfactant, and an alkyl or alkenedimethylamine oxide surfactant; aqueous solutions of an alpha-olefinicsulfonate surfactant and a betaine surfactant; and combinations thereof.Examples of suitable mixtures of an ethoxylated alcohol ether sulfatesurfactant, an alkyl or alkene amidopropyl betaine surfactant, and analkyl or alkene dimethylamine oxide surfactant are described in U.S.Pat. No. 6,063,738, the relevant disclosure of which is incorporatedherein by reference. Examples of suitable aqueous solutions of analpha-olefinic sulfonate surfactant and a betaine surfactant aredescribed in U.S. Pat. No. 5,879,699, the relevant disclosure of whichis incorporated herein by reference. Suitable viscoelastic surfactantsalso may comprise “catanionic” surfactant systems, which comprise pairedoppositely-charged surfactants that act as counterions to each other andmay form wormlike micelles. Examples of such catanionic surfactantsystems include, but are not limited to sodium oleate (NaO)/octyltrimethylammonium chloride (C₈TAC) systems, stearyl trimethylammoniumchloride (C₁₈TAC)/caprylic acid sodium salt (NaCap) systems, and cetyltrimethylammonium tosylate (CTAT)/sodium dodecylbenzenesulfonate (SDBS)systems.

Examples of commercially-available viscoelastic surfactants suitable foruse in the present invention may include, but are not limited to,MIRATAINE BET-O 30™ (an oleamidopropyl betaine surfactant available fromRhodia Inc., Cranbury, N.J.), AROMOX APA-T (amine oxide surfactantavailable from Akzo Nobel Chemicals, Chicago, Ill.), ETHOQUAD O/12 PG™(a fatty amine ethoxylate quat surfactant available from Akzo NobelChemicals, Chicago, Ill.), ETHOMEEN T/12™ (a fatty amine ethoxylatesurfactant available from Akzo Nobel Chemicals, Chicago, Ill.), ETHOMEENS/12™ (a fatty amine ethoxylate surfactant available from Akzo NobelChemicals, Chicago, Ill.), and REWOTERIC TEG™ (a tallow dihydroxyethylbetaine amphoteric surfactant available from Degussa Corp., Parsippany,N.J.).

The viscoelastic surfactant should be present in a fluid of the presentinvention in an amount sufficient to impart the desired viscosity (e.g.,sufficient viscosity to divert flow, reduce fluid loss, suspendparticulates, etc.) to the fluid. In certain embodiments, theviscoelastic surfactant may be present in the fluid in an amount in therange of from about 0.1% to about 20% by weight of the fluid. In certainembodiments, the viscoelastic surfactant may be present in an amount inthe range of from about 0.5% to about 10% by weight of the fluid. Incertain embodiments, the viscoelastic surfactant may be present in anamount in the range of from about 0.5% to about 3% by weight of thefluid.

The amphiphilic polymer(s) used in the present invention may comprise avariety of polymers known in the art that comprise a hydrophobiccomponent and a hydrophilic component. For example, the amphiphilicpolymer(s) may comprise a hydrophobic component, and a hydrophiliccomponent comprising at least 15 monomer units. In certain embodiments,the hydrophilic component may be larger and, for example, have at least20 monomer units. In certain embodiments, the hydrophilic component maybe larger and, for example, have at least 50 monomer units. Examples ofhydrophobic components that may be suitable for use include, but are notlimited to alkyl groups, polybutadiene, polyisoprene, polystyrene,polyoxystyrene, any derivatives thereof, and any combinations thereof.Examples of hydrophilic components that may be suitable for use include,but are not limited to polyethylene oxide (PEO), polyacrylic acid (PAA),polyethylacetate, dimethylacrylamide (DMA), n-isopropylacrylamide(NIPAM), polyvinylpyrrolidone (PVP), polyethyleneimine (PEI), anyderivatives thereof, and any combinations thereof. Examples ofamphiphilic polymers that may be suitable for use include, but are notlimited to polybutadiene-PEO, polystyrene-PEO, polystyrene-polyacrylicacid, polyoxystyrene-PEO, polystyrene-polyethylacetate, any derivativesthereof, and any combinations thereof. Other examples of amphiphilicpolymers that may be suitable for use in the present invention includethose that comprise units based on one or more of the following:acrylamides, vinyl alcohols, vinylpyrrolidones, vinylpyridines,acrylates, polyacrylamides, polyvinyl alcohols, polyvinylpyrrolidones,polyvinylpyridines, polyacrylates, polybutylene succinate, polybutylenesuccinate-co-adipate, polyhydroxybutyrate-valerate,polyhydroxybutyrate-covalerate, polycaprolactones, polyester amides,polyethylene terephthalates, sulfonated polyethylene terephthalate,polyethylene oxides, polyethylenes, polypropylenes, aliphatic aromaticcopolyester, polyacrylic acids, polysaccharides (such as dextran orcellulose), chitins, chitosans, proteins, aliphatic polyesters,polylactic acids, poly(glycolides), poly(ε-caprolactones), poly(hydroxyester ethers), poly(hydroxybutyrates), poly(anhydrides), polycarbonates,poly(orthoesters), poly(amino acids), poly(ethylene oxides),poly(propylene oxides), poly(phosphazenes), polyester amides,polyamides, polystyrenes, any derivative thereof, any copolymer,homopolymer, or terpolymer, or any blend thereof. In certainembodiments, the amphiphilic polymer may comprise a compound selectedfrom the group consisting of hydroxyethyl acrylate, acrylamide andhydroxyethyl methacrylate.

In certain embodiments, the amphiphilic polymer(s) may comprise one ormore alkyl ethoxylates. In certain embodiments, the alkyl ethoxylate maycomprise an alkyl group, and an ethoxylate group having at least 15oxyethylene units. In certain embodiments, the hydrophilic component maybe larger and, for example, have at least 20 oxyethylene units. Incertain embodiments, the hydrophilic component may be larger and, forexample, have at least 50 oxyethylene units. Commercially availablesources of such amphiphilic polymers that may be suitable for use in thepresent invention include, but are not limited to, certain detergentsavailable under the tradename BRIJ®, such as BRIJ®-30 (comprisespolyethylene glycol dodecyl ether), BRIJ®-35 (comprisespolyoxyethyleneglycol dodecyl ether), BRIJ®-58 (comprises polyethyleneglycol hexadecyl ether), BRIJ®-97 (comprises polyoxyethylene (10) oleylether), BRIJ®-98 (comprises polyoxyethylene (20) oleyl ether), andBRIJ®-700 (comprises polyoxyethylene (100) stearyl ether). Othercommercially available sources of such amphiphilic polymers that may besuitable for use in the present invention include, certain detergentsavailable under the tradename IGEPAL®.

The amphiphilic polymer should be present in a fluid of the presentinvention in an amount sufficient to impart the desired viscosity (e.g.,sufficient viscosity to divert flow, reduce fluid loss, suspendparticulates, etc.) to the fluid. In certain embodiments, theamphiphilic polymer may be present in the fluid in an amount in therange of from about 1 mol % to about 5 mol % based on the amount of theviscoelastic surfactant. In certain embodiments, the amphiphilic polymermay be present in the fluid in an amount in the range of from about 1mol % to about 3 mol % based on the amount of the viscoelasticsurfactant. In some instances, the presence of excessive amounts ofamphiphilic polymer may reduce the stability of the viscoelasticsurfactant fluid (e.g., may reduce the viscosity of the fluid). A personof skill in the art, with the benefit of this disclosure, will recognizethe amount of amphiphilic polymer that may produce these effects in aparticular application of the present invention, and determine when theyshould be avoided or employed. For example, certain embodiments of thepresent invention may comprise adding sufficient amounts of theamphiphilic polymer to reduce the viscosity of the fluid, among otherpurposes, to permit the fluid to leak off into a subterranean formation.

The fluids of the present invention generally comprise an aqueous basefluid. Suitable aqueous base fluids may comprise, among other things,fresh water, saltwater (e.g., water containing one or more saltsdissolved therein), brine, seawater, and/or any combination thereof.Generally, the water may be from any source, provided that it does notcontain components that might adversely affect the stability and/orperformance of the fluids of the present invention. In certainembodiments, the density of the aqueous base fluid can be adjusted,among other purposes, to provide additional particle transport andsuspension in the fluids of the present invention and/or to facilitatedissolving the viscoelastic surfactant into the aqueous base fluid. Incertain embodiments, the pH of the aqueous base fluid may be adjusted(e.g., by a buffer or other pH adjusting agent), among other purposes,to reduce the viscosity of the fluid (e.g., activate a breaker or otheradditive). In these embodiments, the pH may be adjusted to a specificlevel, which may depend on, among other factors, the type(s) ofviscoelastic surfactant(s), amphiphilic polymers, salts, and otheradditives included in the fluid. One of ordinary skill in the art, withthe benefit of this disclosure, will recognize when such density and/orpH adjustments are appropriate.

The fluids used in methods of the present invention optionally maycomprise any number of additional additives, including, but not limitedto, salts, co-surfactants, acids, additional fluid loss controladditives, gas, nitrogen, carbon dioxide, surface modifying agents,tackifying agents, foamers, corrosion inhibitors, scale inhibitors,catalysts, clay control agents, biocides, friction reducers, antifoamagents, bridging agents, dispersants, flocculants, H₂S scavengers, CO₂scavengers, oxygen scavengers, lubricants, viscosifiers, breakers,weighting agents, relative permeability modifiers, resins, particulatematerials (e.g., proppant particulates), wetting agents, coatingenhancement agents, and the like. In certain embodiments, the fluids andadditives of the present invention may not comprise a substantial amountof a zwitterionic surfactant. A person skilled in the art, with thebenefit of this disclosure, will recognize the types of additives thatmay be included in the fluids of the present invention for a particularapplication.

For example, the fluids of the present invention optionally may compriseone or more salts. The salts may be organic or inorganic. Examples ofsuitable organic salts include but are not limited to aromaticsulfonates and carboxylates (such as p-toluene sulfonate, naphthalenesulfonate), hydroxynaphthalene carboxylates, salicylate, phthalate,chlorobenzoic acid, salicylic acid, phthalic acid, 5-hydroxy-1-naphthoicacid, 6-hydroxy-1-naphthoic acid, 7-hydroxy-1-naphthoic acid,1-hydroxy-2-naphthoic acid, 3-hydroxy-2-naphthoic acid,5-hydroxy-2-naphthoic acid, 7-hydroxy-2-naphthoic acid,1,3-dihydroxy-2-naphthoic acid, 3,4-dichlorobenzoate, trimethylammoniumhydrochloride and tetramethylammonium chloride. Examples of suitableinorganic salts include water-soluble potassium, sodium, and ammoniumsalts, (such as sodium chloride, potassium chloride, and ammoniumchloride), calcium chloride, calcium bromide, magnesium chloride andzinc halide salts. Examples of viscoelastic surfactant fluids comprisingsalts suitable for use in the present invention are described in U.S.patent application Ser. No. 10/800,478, the relevant disclosure of whichis incorporated herein by reference. Any combination of the salts listedabove also may be included in the fluids of the present invention.

The optional salt may be present in any practicable amount. In certainembodiments, the salt may be present in an amount in the range of fromabout 0.1% to about 30% by weight of the fluid. In certain embodiments,the salt may be present in an amount in the range of from about 0.1% toabout 10% by weight of the fluid. The type(s) and amount of saltssuitable in a particular application of the present invention may dependupon a variety of factors, such as the type(s) of viscoelasticsurfactant(s) present in the fluid, the composition of the aqueous-basefluid, the temperature of the fluid and/or the region of desired use,and the like. In certain embodiments of the present invention, theaqueous base fluid may comprise a brine that already includes a certainamount of salt. In these embodiments, additional salts may not bedesired, or it may be desirable to remove salt from or add further saltto the brine in the preparation and/or use of a fluid of the presentinvention. A person of ordinary skill, with the benefit of thisdisclosure, will recognize when to include a salt in a particularapplication of the present invention, as well as the appropriate typeand amount of salts to include.

In certain embodiments, the methods of the present invention generallycomprise: providing an aqueous base fluid, a viscoelastic surfactant,and an amphiphilic polymer that comprises (a) a hydrophobic componentcomprising an alkyl group, and (b) a hydrophilic component comprising anethoxylate having at least 20 oxyethylene units; and mixing the aqueousbase fluid, the viscoelastic surfactant, and the amphiphilic polymertogether to form a fluid of the present invention. The fluids of thepresent invention and/or any component thereof (e.g., the amphiphilicpolymer) may be provided in any form that is suitable for the particularapplication of the present invention. In certain embodiments, theviscoelastic surfactant and/or amphiphilic polymer may be provided as aliquid and/or solid additive that is admixed or incorporated at anypoint prior to and/or during use of the fluid. For example, in certainembodiments, the amphiphilic polymer may be added to a fluid that isalready present in a portion of a subterranean formation. The differentcomponents of the fluids of the present invention may be provided orincorporated together (e.g., in the same additive or fluid), or they maybe provided or incorporated into a fluid as separate additives. Wherethey are provided or incorporated into a fluid separately, the differentcomponents may be provided or incorporated simultaneously, or certaincomponents may be provided or incorporated at some point in time beforeor after the other components are provided or incorporated. The fluidsof the present invention and/or any component thereof may be prepared ata job site, or they may be prepared at a plant or facility prior to use,and may be stored for some period of time prior to use. In certainembodiments, the preparation of these fluids of the present inventionmay be done at the job site in a method characterized as being performed“on the fly.” The term “on-the-fly” is used herein to include methods ofcombining two or more components wherein a flowing stream of one elementis continuously introduced into flowing stream of another component sothat the streams are combined and mixed while continuing to flow as asingle stream as part of the on-going treatment. Such mixing can also bedescribed as “real-time” mixing.

In certain embodiments, the methods of the present invention comprise:providing a treatment fluid that comprises an aqueous base fluid, aviscoelastic surfactant, and an amphiphilic polymer that comprises (a) ahydrophobic component comprising an alkyl group, and (b) a hydrophiliccomponent comprising an ethoxylate having at least 15 oxyethylene units;and introducing the treatment fluid into at least a portion of asubterranean formation. In these methods, the treatment fluid (and/orthe separate components thereof) may be introduced into a portion of asubterranean formation by any means known in the art.

The methods and treatment fluids of the present invention may be usedduring or in preparation for any subterranean operation wherein a fluidmay be used. Suitable subterranean operations may include, but are notlimited to, preflush treatments, afterflush treatments, drillingoperations, hydraulic fracturing treatments, sand control treatments(e.g., gravel packing), acidizing treatments (e.g., matrix acidizing orfracture acidizing), “frac-pack” treatments, well bore clean-outtreatments, and other operations where a treatment fluid of the presentinvention may be useful. For example, in certain embodiments, thepresent invention provides fluids that comprise an aqueous base fluid, aviscoelastic surfactant, an amphiphilic polymer that comprises (a) ahydrophobic component comprising an alkyl group, and (b) a hydrophiliccomponent comprising an ethoxylate having at least 15 oxyethylene units,and, in certain embodiments, a plurality of proppant particulates. Incertain embodiments, a treatment fluid of the present invention may beused in a method of fracturing a subterranean formation, wherein atreatment fluid of the present invention is introduced into thesubterranean formation at or above a sufficient hydraulic pressure tocreate or enhance one or more cracks, or “fractures,” in thesubterranean formation. “Enhancing” one or more fractures in asubterranean formation, as that term is used herein, is defined toinclude the extension or enlargement of one or more natural orpreviously created fractures in the subterranean formation. This may,among other things, form conductive channels in the subterraneanformation through which fluids (e.g., oil, gas, etc.) may flow to a wellbore penetrating the subterranean formation.

To facilitate a better understanding of the present invention, thefollowing examples of certain aspects of some embodiments are given. Inno way should the following examples be read to limit, or define, theentire scope of the invention.

EXAMPLES Example 1A

A fluid was prepared comprising a 1.5% by weight aqueous solution of acetyl trimethylammonium tosylate (CTAT)/sodium dodecylbenzenesulfonate(SDBS) (97:3 weight ratio) surfactant system, and the zero-shearviscosity of the fluid was measured using an Physica MCR501 rheometer(manufactured by Anton Paar GmbH) at 70° F. and ambient pressure. Acertain amount of an amphiphilic polymer (BRIJ-35 or BRIJ-700) was thenadded to 3 different samples of that fluid, and the zero-shear viscosityof each fluid sample with the polymer added was measured at the sameconditions. The types and amounts (by weight of the surfactant system)of amphiphilic polymer added to each fluid and the resulting viscositiesare listed in Table 1 and depicted in FIG. 1.

TABLE 1 Fluid Sample Zero shear viscosity No. Composition (Pa * s) ACTAT/SDBS surfactant 282 B CTAT/SDBS surfactant + 1 mol % 231 BRIJ-35 CCTAT/SDBS surfactant + 1 mol % 215 BRIJ-700 D CTAT/SDBS surfactant + 3mol % 23 BRIJ-700

Example 1B

A second fluid was prepared using the same surfactant system andconcentration described in Example 1A in an aqueous 0.7M solution ofsodium bromide (NaBr), and its zero-shear viscosity was measured. Anamphiphilic polymer (BRIJ-700) was added to 2 different samples of thatfluid (1 mol % and 3 mol % by weight of the surfactant system,respectively), and the zero-shear viscosity of each fluid sample withthe polymer added was measured. The resulting viscosities are listed inTable 2 and are depicted in FIG. 2, along with the zero-shear viscosityof the initial fluid from Example 1A without polymer or sodium bromidefor comparison.

TABLE 2 Fluid Sample No. Composition Zero shear viscosity (Pa * s) ECTAT/SDBS surfactant 282 (from Example 1A) F 0.7M NaBr + CTAT/SDBS 1.7surfactant G 0.7M NaBr + CTAT/SDBS 5.8 surfactant + 1 mol % BRIJ-700 H0.7M NaBr + CTAT/SDBS 37 surfactant + 3 mol % BRIJ-700

Example 1C

A third fluid was prepared using the same surfactant system andconcentration described in Example 1A in an aqueous 1M solution ofsodium bromide (NaBr). An amphiphilic polymer (BRIJ-700) was added to 2different samples of that fluid (1 mol % and 3 mol % by weight of thesurfactant system, respectively), and the zero-shear viscosity of eachfluid sample with the polymer added was measured. The resultingviscosities are listed in Table 3 and are depicted in FIG. 3, along withthe zero-shear viscosity of the initial fluid from Example 1A withoutpolymer or sodium bromide for comparison.

TABLE 3 Fluid Sample No. Composition Zero shear viscosity (Pa * s) ICTAT/SDBS surfactant 282 (from Example 1A) J 1M NaBr + CTAT/SDBS 6.8surfactant + 1 mol % BRIJ-700 K 1M NaBr + CTAT/SDBS 35 surfactant + 3mol % BRIJ-700

Example 1D

A fourth fluid was prepared using the same surfactant system andconcentration described in Example 1A in an aqueous 2M solution ofsodium bromide (NaBr). An amphiphilic polymer (BRIJ-700) was added thefluid (3 mol % by weight of the surfactant system), and the zero-shearviscosity of the fluid with the polymer added was measured. Theresulting viscosities are listed in Table 4 and are depicted in FIG. 4,along with the zero-shear viscosity of the initial fluid from Example 1Awithout any polymer or sodium bromide for comparison.

TABLE 4 Fluid Sample No. Composition Zero shear viscosity (Pa * s) LCTAT/SDBS surfactant 282 (from Example 1A) M 2M NaBr + CTAT/SDBS 3.1surfactant N 2M NaBr + CTAT/SDBS 33 surfactant + 3 mol % BRIJ-700

Thus, Examples 1A-1D illustrate that the methods and additives of thepresent invention may enhance the rheology of certain viscoelasticsurfactant fluids.

Example 2A

A fluid was prepared comprising a 3% by weight aqueous solution of acetyl trimethylammonium tosylate (CTAT)/sodium dodecylbenzenesulfonate(SDBS) (97:3 weight ratio) surfactant system, and the zero-shearviscosity of the fluid was measured using the same methods andparameters described in Example 1A. An amphiphilic polymer (BRIJ-35 orBRIJ-700) was then added to 2 different samples of that fluid (1 mol %by weight of the surfactant system in each), and the zero-shearviscosity of each fluid sample with the polymer added was measured. Theresulting viscosities are listed in Table 5 and depicted in FIG. 5.

TABLE 5 Fluid Sample Zero shear viscosity No. Composition (Pa * s) OCTAT/SDBS surfactant 488 P CTAT/SDBS surfactant + 1 mol % 436 BRIJ-35 QCTAT/SDBS surfactant + 1 mol % 573 BRIJ-700

Example 2B

A second fluid was prepared using the same surfactant system andconcentration described in Example 2A in an aqueous 0.7M solution ofsodium bromide (NaBr), and its zero-shear viscosity was measured. Anamphiphilic polymer (BRIJ-700) was added to the fluid (1 mol % by weightof the surfactant system), and the zero-shear viscosity of the fluidwith the polymer added was measured. The resulting viscosities arelisted in Table 6 and are depicted in FIG. 6, along with the zero-shearviscosity of the initial fluid from Example 2A without polymer or sodiumbromide for comparison.

TABLE 6 Fluid Sample No. Composition Zero shear viscosity (Pa * s) RCTAT/SDBS surfactant 488 S 0.7M NaBr + CTAT/SDBS 4.3 surfactant T 0.7MNaBr + CTAT/SDBS 16.7 surfactant + 1 mol % BRIJ-700

Thus, Examples 2A and 2B illustrate that the methods and additives ofthe present invention may enhance the rheology of certain viscoelasticsurfactant fluids.

Example 3A

A fluid was prepared comprising a 3% by weight aqueous solution of asodium oleate (NaO)/octyl trimethylammonium chloride (C₈TAC) (7:3 weightratio) surfactant system, and the zero-shear viscosity of the fluid wasmeasured using the same methods and parameters described in Example 1A.An amphiphilic polymer (BRIJ-30, BRIJ-35, or BRIJ-700) was then added to3 different samples of that fluid (1 mol % by weight of the surfactantsystem in each), and the zero-shear viscosity of each fluid sample withthe polymer added was measured. The resulting viscosities are listed inTable 7 and depicted in FIG. 7.

TABLE 7 Fluid Sample Zero shear viscosity No. Composition (Pa * s) UNaO/C₈TAC surfactant 1180 V NaO/C₈TAC surfactant + 1 mol % 41 BRIJ-30 WNaO/C₈TAC surfactant + 1 mol % 154 BRIJ-35 X NaO/C₈TAC surfactant + 1mol % 629 BRIJ-700

Example 3B

A second fluid was prepared using the same surfactant system andconcentration described in Example 3A in an aqueous 0.15M solution ofsodium bromide (NaBr), and its zero-shear viscosity was measured. Anamphiphilic polymer (BRIJ-700) was added to the fluid (1 mol % by weightof the surfactant system), and further sodium bromide was added to bringthe solution to a 0.2M NaBr concentration. The zero-shear viscosity ofthe fluid with the polymer and additional NaBr was measured. Theresulting viscosities are listed in Table 8 and are depicted in FIG. 8,along with the zero-shear viscosity of the initial fluid from Example 3Awithout polymer or sodium bromide for comparison.

TABLE 8 Fluid Sample No. Composition Zero shear viscosity (Pa * s) YNaO/C₈TAC surfactant 1180 Z 0.15M NaBr + NaO/C₈TAC 2.4 surfactant AA0.2M NaBr + NaO/C₈TAC 24 surfactant + 1 mol % BRIJ-700

Thus, Examples 3A and 3B illustrate that the methods and additives ofthe present invention may enhance the rheology of certain viscoelasticsurfactant fluids.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Furthermore, no limitations areintended to the details of construction or design herein shown, otherthan as described in the claims below. It is therefore evident that theparticular illustrative embodiments disclosed above may be altered ormodified and all such variations are considered within the scope andspirit of the present invention. While compositions and methods aredescribed in terms of “comprising,” “containing,” or “including” variouscomponents or steps, the compositions and methods can also “consistessentially of” or “consist of” the various components and steps. Allnumbers and ranges disclosed above may vary by some amount. Whenever anumerical range with a lower limit and an upper limit is disclosed, anynumber and any included range falling within the range is specificallydisclosed. In particular, every range of values (of the form, “fromabout a to about b,” or, equivalently, “from approximately a to b,” or,equivalently, “from approximately a-b”) disclosed herein is to beunderstood to set forth every number and range encompassed within thebroader range of values. Also, the terms in the claims have their plain,ordinary meaning unless otherwise explicitly and clearly defined by thepatentee. Moreover, the indefinite articles “a” or “an”, as used in theclaims, are defined herein to mean one or more than one of the elementthat it introduces. If there is any conflict in the usages of a word orterm in this specification and one or more patent or other documentsthat may be incorporated herein by reference, the definitions that areconsistent with this specification should be adopted.

What is claimed is:
 1. A method comprising: providing a treatment fluidthat comprises an aqueous base fluid, a viscoelastic surfactant, and anamphiphilic polymer, the amphiphilic polymer comprising: a hydrophobiccomponent, and a hydrophilic component itself comprising at least 15monomer units; wherein the amphiphilic polymer comprises: a hydrophobiccomponent selected from the group consisting of polybutadiene,polyisoprene, polystyrene, and combinations thereof, and, a hydrophiliccomponent selected from the group consisting of an ethoxylate,polyethylene oxide (PEO), polyacrylic acid (PAA), polyethylacetate,dimethylacrylamide (DMA), n-isopropylacrylamide (NIPAM),polyvinylpyrrolidone (PVP), polyethyleneimine (PEI), derivativesthereof, and combinations thereof; and, introducing the treatment fluidinto at least a portion of a subterranean formation.
 2. The method ofclaim 1 wherein the amphiphilic polymer comprises an alkyl ethoxylatecomprising at least 15 oxyethylene units.
 3. The method of claim 1wherein the aqueous base fluid comprises at least one brine.
 4. Themethod of claim 1 wherein the viscoelastic surfactant comprises at leastone surfactant selected from the group consisting of: a methyl estersulfonate, a hydrolyzed keratin, a sulfosuccinate, a taurate, an amineoxide, an ethoxylated amide, an alkoxylated fatty acid, an alkoxylatedalcohol, an ethoxylated fatty amine, an ethoxylated alkyl amine, abetaine, a modified betaine, an alkylamidobetaine, a quaternary ammoniumcompound, any derivative thereof, and any combination thereof.
 5. Themethod of claim 1 wherein the treatment fluid does not comprise azwitterionic surfactant.
 6. The method of claim 1 wherein theviscoelastic surfactant comprises a catanionic surfactant system.
 7. Themethod of claim 1 wherein the viscoelastic surfactant is present in thetreatment fluid in an amount of from about 0.1% to about 20% by weightof the treatment fluid.
 8. The method of claim 1 wherein the amphiphilicpolymer is present in the treatment fluid in an amount of from about 1mol % to about 5 mol % based on the amount of the viscoelasticsurfactant.
 9. The method of claim 1 wherein the treatment fluid furthercomprises at least one salt.
 10. The method of claim 1 whereinintroducing the treatment fluid into at least a portion of asubterranean formation comprises introducing the treatment fluid intothe subterranean formation at or above a pressure sufficient to createor enhance one or more cracks or fractures in at least a portion of thesubterranean formation.
 11. A method comprising: providing a treatmentfluid that comprises an aqueous base fluid, a viscoelastic surfactant,and an amphiphilic polymer, the amphiphilic polymer comprising ahydrophobic component and a hydrophilic component: the hydrophiliccomponent comprising at least 15 monomer units; a hydrophobic componentselected from the group consisting of polybutadiene, polyisoprene, andcombinations thereof, and, a hydrophilic component selected from thegroup consisting of an polyethylacetate, dimethylacrylamide (DMA),n-isopropylacrylamide (NIPAM), polyethyleneimine (PEI), and combinationsthereof; and, wherein the treatment fluid does not comprise azwitterionic surfactant; and introducing the treatment fluid into atleast a portion of a subterranean formation.
 12. The method of claim 11wherein the aqueous base fluid comprises at least one brine.
 13. Themethod of claim 11 wherein the alkyl ethoxylate comprises at least 15oxyethylene units.